1. Field of the Invention
The present invention relates to a method of controlling a secondary battery.
2. Description of the Related Art
In recent years, approaches to efficiently use energy by use of secondary batteries such as lithium ion batteries, as vehicle on-board power supplies or power supplies for power storage of smart houses have been made. However, the secondary batteries are known to cause characteristic deterioration by charge/discharge or storage. The power supplies of the above intended purposes are expected to be used for a long time. Therefore, it is important to suppress the characteristic deterioration of the secondary batteries. Further, it is important to continuously use the secondary batteries in a safe manner.
The characteristic deterioration and a decrease in safety of the secondary batteries are known to be quickly advanced when voltages of the secondary batteries are too high or too low. In reality, the voltage of the secondary battery is mere a difference between a positive electrode potential and a negative electrode potential of the secondary battery, and the speed of the characteristic deterioration and the decrease in safety is determined by the positive electrode potential and the negative electrode potential, rather than the battery voltage. Therefore, as means for suppressing the deterioration, it is effective to accurately detect the positive and negative electrode potentials in the secondary battery, and to select an optimum method of using the battery according to the detected potentials.
For example, JP-2009-80093-A describes a method of quantitatively evaluating deterioration states of positive and negative electrodes and an electrolytic solution in a nondestructive manner, by using a charge/discharge curve of a secondary battery, and determining open circuit potentials of the positive electrode and the negative electrode.